The present invention is directed to a roll having adjustable press zones, such as a roll used in the dewatering press of a paper machine or a calender roll. Such a roll comprises a non-revolving massive central axle, on which a cylindrical roll mantle is rotatably journalled, with a piston-cylinder group or block loading arrangement being fitted between the central axle and an inner face of the roll mantle. In such an arrangement, outer loading pistons can be loaded by means of pressure from hydraulic fluid against the inner face of the roll mantle, so as to adjust the distribution of pressure in zones of a nip formed with the roll on an opposite side of the mantle from the loading pistons, i.e. in a nip facing the loading pistons.
In paper machines, several such rolls are used to form a dewatering press nip, or a smoothing nip, or a calendering nip with a counter-roll. In these applications, it is important for distribution or profile of linear load in the nip to remain constant in the axial direction of the rolls, or for the pressure profile to be adjusted as desired, e.g., so as to control the moisture profile and/or the thickness profile of the web in the transverse direction. For this purpose, different adjustable-crown or variable-crown rolls have been known in the prior art, by means of which attempts are made to affect distribution of the linear load in a nip.
In the prior art, several different variable-crown or adjustable-crown rolls for paper machines are known. As a rule, these rolls comprise a massive, stationary roll axle and a roll mantle arranged to be rotatable about the axle. Between the axle and mantle, glide shoe arrangements and/or pressure fluid chambers acting upon the inner face of the mantle are fitted, and are divided into several parts over the axial direction of the roll, so that the axial profile of the mantle at the nip can be straightened or adjusted as desired. As a rule, nips formed by such rolls, such as press nips or calendering nips, are loaded by means of loading forces directed at the axle journals of the adjustable-crown roll and of its counter-roll. The present invention is related to such variable-crown rolls, including a series of glide shoes having glide faces which are hydrostatically lubricated by means of pressure fluid passed onto the glide face.
With respect to prior art technology, reference is made by way of example, to DE Pat. Nos. 2,838,427 and 3,022,491, to FI Pat. No. 59,655, and to FI Applications Nos. 2703/73 and 760117. From the supporting and loading members used in variable-crown rolls, acting upon the inner face of the roll mantle and loaded by means of pressure fluid, a great number of functions of different nature are required, the integration thereof in the same member not having been fully successful by means of the arrangements known in the prior art. A list of certain properties required of the supporting and loading members, is given as follows:
The hydrostatic lubrication of the support member, as well as of the loading piston/cylinder must be sufficiently well-sealed, even with varying loading forces and when an angular change occurs between the roll mantle and the inner part;
The loading pistons of the support members must receive lateral forces, which are friction forces;
The loading equipment of the support member must be capable of acting as an articulated joint, because the relative positions of the mantle to be supported and the central axle vary to a considerable extent as the loading forces vary;
The pistons of the support member must yield sufficient radial force, whose range of variation is relatively large in order to support and to load the mantle;
It must be possible to control the thickness of the oil film that lubricates the glide face of the support member; and
The bore placed in connection with the pistons of the support member, and the pistons of the support member itself, must permit even considerable radial movements of the pistons.
In the prior art supporting and loading members, certain of the functions or characteristics listed above are not accomplished satisfactorily. Certainly, all of the functions listed above are not accomplished satisfactorily together. Thus, an object of the present invention is to avoid the drawbacks present in these prior art devices, and to provide a novel roll structure for the purposes concerned.
The prior-art glide shoes for variable-crown rolls, based on hydrodynamic lubrication, have involved, for example, the drawback that at a low speed, the lubrication is not sufficiently effective. It is partially due to this previously-encountered drawback that, in the present invention, efforts have been taken for further development of rolls which are adjustable in zones expressly based on hydrostatic glide shoes.
As follows from the above, a commonly used construction of a press roll adjustable in zones is such that the cylinders of the press pistons acting upon the inner face of the revolving mantle are stationary in relation to the massive central axle of the roll. Such cylinders, as a rule, consist of bores made into the central axle itself. This results in the drawback that when the central axle is deflected, the position and direction of the cylinders are also altered, which then affects the loading pistons of the cylinders in the form of changes in direction and position. These changes then deteriorate the mutual lubricated glide contact between the pistons and the revolving cylinder mantle.
In order to eliminate these problems, a great number of different sealing and articulation arrangements between the loading pistons and the cylinders thereof have been created. However, all of these have been characterized by complicated construction and operational deficiencies.